Work machines, such as tractors, utilized, for instance, for agriculture, construction, mining, earth-moving, and the like, are not typically powered in the same manner as road vehicles. In a work machine the throttle is used to increase engine speed to provide power to drive the work machine at a particular ground speed and to provide power to one or more other systems of the machine. It is advantageous to have the capability to operate these work machines under conditions where their engine speed is held closely to a setting set by the operator. However, many work machines are subjected to rapidly occurring and widely varying load conditions that require engine speed adjustments so as to make known ground speed cruise control systems unsatisfactory for use in automatic engine speed control systems.
Upper limit control of engine speed in a work machine would be desirable as it can help protect an engine from damage caused by abrupt machine unload conditions. In a most desired form, an upper limit engine speed control would allow an operator to set and adjust an engine speed upper limit that optimizes engine performance based on the work being performed by the machine. As work conditions change, for example, if the machine were to encounter an increased load, such as a tractor entering a more densely populated crop area, the operator would be able to increase the throttle position to maintain the optimized engine speed, and when the load returns to normal, the increased throttle position command would be limited by the engine speed control system without resetting the upper limit, exiting the system, or requiring repositioning of the throttle. If the machine were to encounter a decreased load, such as a tractor nearing the end of a swath of field, the operator would decrease engine speed from the optimized speed used for the field work, move to the next swath of the field, and continue working at the previously set, optimized engine speed without exiting the engine speed control mode. These capabilities are not achieved by known cruise control systems which focus on ground speeds.
Additionally, lower limit control of engine speed in a work machine would be desirable to help protect an engine from a stall condition caused by abrupt machine load conditions. Lower limit engine speed control would allow an operator to set and adjust an engine speed lower limit that optimizes engine performance based on the work being performed by the machine. For example, if the machine were to encounter an increased load, such as a tractor entering a more densely populated crop area, it would be desirable to have the capability for the operator to increase the throttle position to maintain the optimized engine speed, and when the load returns to normal, wherein if the operator removes the throttle input, and the throttle position command is limited by the engine speed control system without resetting the lower limit, or exiting the system. Again, because known cruise control system focus on ground speed of the vehicle, these capabilities are not achieved by known systems.
It would also be desirable for the operator to have the capability to adjust for varying load conditions during work, in real time, by allowing upward and downward adjustments of the designated engine speed limits without much effort.
One system, such as the one described in Linden et al., U.S. Pat. No. 5,713,428 discloses a ground speed control system with a cruise control mode and a mutually exclusive upper speed limitation mode. While this system may be useful for motor vehicles, it does not provide for engine speed control as required for work machines. The transmission systems in motor vehicles allow for wildly varying engine speeds to correspond to similar ground speed.
It is therefore desirable to have an engine speed control system with a mode which allows engine speed operation at or below an operator adjustable upper limit and a mode which allows engine speed operation at or above an operator adjustable lower limit which is simple and easy to operate and otherwise provides one or more of the advantages, benefits, or sought after capabilities or overcomes one or more of the shortcomings set forth above.